Float-operated vapor vent valves are often used in fuel tanks to control fuel vapor flow from the fuel tank to a vapor storage device, such as a canister filled with granulated carbonaceous material. Vapor may be controlled by attaching vapor management valves, such as a fuel limit vent valve and grade vent valves to the fuel tank. Typically, each valve is installed separately to the fuel tank by forming an opening in the fuel tank, inserting the valve into the opening, and sealing the valve to the opening to prevent leakage of fuel or fuel vapor.
To reduce fuel vapor permeation and the number of openings in the fuel tank, multi-function vapor valve assemblies are known to provide the functions of two or more valves in a common assembly to be attached to the fuel tank through a single access opening, or otherwise mounted in the fuel tank. Such multi-function control valves often include multiple float operated valves that open and close different sized vent ports at different liquid fuel levels in the tank during refueling and in response to fuel sloshing in the tank during vehicle operation.
An additional valve may be included to provide a first orifice that restricts vapor flow from the fuel tank during running conditions. This minimizes abrupt changes in vapor flow and allows more aggressive vapor purging, preventing tail pipe emissions caused by spikes in the fuel vapor level down a purge line. The valve assembly may also include a second orifice that manages vapor recirculation during refueling. The many functions required by the multi-function valve assemblies and the number of valves and flow paths resulting from the functions tend to increase both the size and the complexity of the valve assembly. The way in which the valves communicate with each other and operate relative to different fuel levels and vapor pressures in the fuel tank often requires complicated routing of fuel vapors around and through the various valves to obtain the desired functions.